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Fix possible write stall

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The stall occurred during fio Q=128 random write tests with low flusher_count (4).
It was caused by flushers being unable to flush the beginning of the journal
because it contained older writes to an object that also had writes in the very end
of the journal, after dirty_start.
This commit is contained in:
Vitaliy Filippov
2020-06-01 16:18:23 +03:00
parent c22e096943
commit e6a4b634f8
5 changed files with 86 additions and 16 deletions
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blockstore_flush.cpp
+76 -13
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@@ -7,8 +7,8 @@ journal_flusher_t::journal_flusher_t(int flusher_count, blockstore_impl_t *bs)
dequeuing = false;
active_flushers = 0;
syncing_flushers = 0;
sync_threshold = bs->journal_block_size / sizeof(journal_entry_stable);
journal_trim_interval = sync_threshold;
flusher_start_threshold = bs->journal_block_size / sizeof(journal_entry_stable);
journal_trim_interval = flusher_start_threshold;
journal_trim_counter = 0;
journal_superblock = bs->journal.inmemory ? bs->journal.buffer : memalign(MEM_ALIGNMENT, bs->journal_block_size);
co = new journal_flusher_co[flusher_count];
@@ -81,7 +81,7 @@ void journal_flusher_t::enqueue_flush(obj_ver_id ov)
flush_versions[ov.oid] = ov.version;
flush_queue.push_back(ov.oid);
}
if (!dequeuing && flush_queue.size() >= sync_threshold)
if (!dequeuing && flush_queue.size() >= flusher_start_threshold)
{
dequeuing = true;
bs->ringloop->wakeup();
@@ -101,19 +101,25 @@ void journal_flusher_t::unshift_flush(obj_ver_id ov)
flush_versions[ov.oid] = ov.version;
flush_queue.push_front(ov.oid);
}
if (!dequeuing && flush_queue.size() >= sync_threshold)
if (!dequeuing && flush_queue.size() >= flusher_start_threshold)
{
dequeuing = true;
bs->ringloop->wakeup();
}
}
void journal_flusher_t::force_start()
void journal_flusher_t::request_trim()
{
dequeuing = true;
trim_wanted++;
bs->ringloop->wakeup();
}
void journal_flusher_t::release_trim()
{
trim_wanted--;
}
#define await_sqe(label) \
resume_##label:\
sqe = bs->get_sqe();\
@@ -181,14 +187,71 @@ resume_0:
(bs->journal.dirty_start >= bs->journal.used_start ||
dirty_end->second.journal_sector < bs->journal.used_start))
{
// We can't flush journal sectors that are still written to
#ifdef BLOCKSTORE_DEBUG
printf("Flusher overran writers - stopping\n");
#endif
flusher->enqueue_flush(cur);
flusher->dequeuing = false;
wait_state = 0;
return true;
// We can't flush journal sectors that are still written to
// However, as we group flushes by oid, current oid may have older writes to flush!
// And it may even block writes if we don't flush the older version
// (if it's in the beginning of the journal)...
// So first try to find an older version of the same object to flush.
bool found = false;
while (dirty_end != bs->dirty_db.begin())
{
dirty_end--;
if (dirty_end->first.oid != cur.oid)
{
break;
}
if (!(dirty_end->second.journal_sector >= bs->journal.dirty_start &&
(bs->journal.dirty_start >= bs->journal.used_start ||
dirty_end->second.journal_sector < bs->journal.used_start)))
{
found = true;
cur.version = dirty_end->first.version;
break;
}
}
if (!found)
{
// Try other objects
int search_left = flusher->flush_queue.size() - 1;
#ifdef BLOCKSTORE_DEBUG
printf("Flusher overran writers (dirty_start=%08lx) - searching for older flushes (%d left)\n", bs->journal.dirty_start, search_left);
#endif
while (search_left > 0)
{
cur.oid = flusher->flush_queue.front();
cur.version = flusher->flush_versions[cur.oid];
flusher->flush_queue.pop_front();
flusher->flush_versions.erase(cur.oid);
dirty_end = bs->dirty_db.find(cur);
if (dirty_end != bs->dirty_db.end())
{
if (dirty_end->second.journal_sector >= bs->journal.dirty_start &&
(bs->journal.dirty_start >= bs->journal.used_start ||
dirty_end->second.journal_sector < bs->journal.used_start))
{
#ifdef BLOCKSTORE_DEBUG
printf("Write %lu:%lu v%lu is too new: offset=%08lx\n", cur.oid.inode, cur.oid.stripe, cur.version, dirty_end->second.journal_sector);
#endif
flusher->enqueue_flush(cur);
}
else
{
break;
}
}
search_left--;
}
if (search_left <= 0)
{
#ifdef BLOCKSTORE_DEBUG
printf("No older flushes, stopping\n");
#endif
flusher->dequeuing = false;
wait_state = 0;
return true;
}
}
}
repeat_it = flusher->sync_to_repeat.find(cur.oid);
if (repeat_it != flusher->sync_to_repeat.end())
@@ -409,7 +472,7 @@ resume_1:
// Update clean_db and dirty_db, free old data locations
update_clean_db();
// Clear unused part of the journal every <journal_trim_interval> flushes
if (!((++flusher->journal_trim_counter) % flusher->journal_trim_interval))
if (!((++flusher->journal_trim_counter) % flusher->journal_trim_interval) || flusher->trim_wanted > 0)
{
flusher->journal_trim_counter = 0;
if (bs->journal.trim())